Involvement of a Na−Ca exchange mechanism in contraction induced by low-Na solution in isolated guinea-pig aorta

The possibility of involvement of a Na–Ca exchange mechanism in the contractile responses induced by a reduction of external Na concentration ([Na]₀) has been studied in isolated guinea-pig aorta. Low-Na (11.9 mM) solution (Lisubstituted) produced a contraction in ouabain-treated muscles in the presence of phentolamine (10^–6 M). The magnitude of the contraction was dependent on the duration of the pretreatment with ouabain (2×10^–5 M). Ca-free solution, but not verapamil (10^–6 M), abolished the contraction induced by low-Na solution. The muscles were loaded with various amounts of Na by incubating the tissue with ouabain and varying [Na]₀ (11.9–148.7 mM) in the absence of Ca. The magnitude of the contractions induced in these muscles by low-Na solution containing Ca (2.5 mM) was dependent on the cellular Na content. Loss of cellular Na into low-Na solution followed a single exponential time course and the rate coefficient of Na-loss in the presence of external Ca was about twice as great as in the absence of Ca. Cellular⁴⁵Ca uptake in low-Na solution was significantly greater in Na-loaded tissues (pretreated with ouabain for 3 h) than in normal tissues. The⁴⁵Ca uptake in low-Na solution was not inhibited by verapamil. These results suggest that the contraction induced by low-Na solution is caused by a Ca influx which is dependent on internal Na (a Na–Ca exchange mechanism).     

Caffeine actions on currents induced by calcium-overload in Purkinje fibers

The ionic events underlying the changes induced by caffeine in calcium-overloaded Purkinje fibers were studied by means of a voltage-clamp technique. The following results were obtained. In fibers exposed to strophanthidin (5 X 10(-7) M), a depolarizing clamp of suitable magnitude or duration is followed by an oscillatory current (Ios) often superimposed on a decaying inward tail current (the "tail current"). Caffeine (9 mM) abolishes Ios and increases the tail current. Caffeine has similar actions when calcium overload is induced by increasing [Ca]0 or decreasing [Na]0. The magnitude of the tail current is reduced by decreasing [Ca]0. The tail current appears with repolarizations to -40 mV or more negative values as Ios appears in the absence of caffeine. As with Ios the tail current can be triggered twice (during and after a test clamp of suitable characteristics), becomes more inward with repeated clamps and becomes larger with larger or longer conditioning clamps. During the recovery from caffeine exposure, the tail current decreases gradually as Ios returns progressively. It is concluded that both Ios and tail current are caused by calcium overload but are affected in opposite direction by caffeine, apparently because caffeine decreases the calcium overload in the sarcoplasmic reticulum (abolition of Ios) and increases the calcium to be extruded from the sarcoplasm (increase in the tail current).     

Placental transfer and fetal distribution of cadmium and mercury after treatment with dithiocarbamates

The distribution in pregnant C57BL mice (day 18 of gestation) of intravenously administered cadmium (Cd) chloride and mercury (Hg) chloride (0.75 mol/kg b.w.) was studied, with or without previous dithiocarbamate pretreatment. Diethyldithiocarbamate (DEDTC), disulfiram, or thiram (2×1 mmol/kg b.w.) or vehicle (gelatine) alone, were given by gavage 2 h before and immediately after injection of the metals. The mice were sacrificed 4 and 24 h later and subjected to autoradiography or impulse counting of excised organs.All the dithiocarbamates increased the concentration of both Cd and Hg in brain and most other maternal organs. While DEDTC and thiram, in that order, strongly increased Cd concentrations in whole fetuses (around 17-fold at 4 h) and all fetal organs measured, disulfiram caused a decrease in fetal Cd concentrations. For Hg, all the dithiocarbamates substantially decreased fetal levels. Disulfiram, for example, decreased Hg levels by a factor of 5. The 24 h values confirmed those at 4 h both elements, although the differences between control and treatment groups were less pronounced.Although the results suggest the formation of lipid-soluble metal-dithiocarbamate complexes in vivo (e.g., increased concentration in brain), this does not necessarily lead to increased fetal levels of the metals. The increased levels of Cd after thiram and DEDTC pretreatment, however, indicate a risk for higher Cd fetotoxicity. It is likely that Cd is released in fetal cells following metabolism of the dithiocarbamate moiety of the complex.     

信息交流视角下国内外科技期刊的知识服务模式

【目的】在信息交流视角下,探讨我国科技期刊知识服务转型发展的突破路径。 【方法】通过文献调研和对比分析法,探讨面向科技期刊知识服务的科学信息交流模式框架,对国内外科技期刊知识服务模式进行分析。 【结果】分别从正式交流和非正式交流视角,归纳总结国内外科技期刊所开展的知识服务。通过对比国内外科技期刊在服务模式、手段和渠道的差异,提出我国科技期刊知识服务的发展策略。 【结论】我国科技期刊应从集团化经营模式、自动化出版流程、基于微信矩阵拓展服务项目等方面入手,完善自身的知识服务体系,实现知识生产向知识服务的创新转型。     

梧桐花粉主要变反原的分离纯化

以离子交换和凝胶过滤层析对梧桐花粉变应原进行分离和纯化,采用生物素-链霉亲和素酶联免疫吸附分析法（BSA-ELISA）测定其抗原活性,得到两个具高活性的单一变应原组分PT13和PT53。经SDS-聚丙烯酰胺凝胶电泳测得它们的分子质量分别为20ku和18ku。     

Update on ENT anaesthesia in children

This article is an update of anaesthesia for common paediatric ear, nose and throat (ENT) procedures. ENT pathology is the most common indication for surgery in children. An increasing proportion are performed as day cases, even in the presence of comorbidities such as obstructive sleep apnoea (OSA), so judicious selection of suitable children remains important. Considerations include severity of disease, known difficult airway, complex comorbidities, and the surgical centre. The anaesthetic management of frequently performed paediatric ENT procedures will be discussed, including recent advances in ENT surgery that have an impact on the anaesthetist.     

Characterization of butyrate-dependent electroneutral Na-Cl absorption in the rat distal colon

Recent studies have established that mucosal butyrate stimulates electroneutral sodium-chloride (NaCl) absorption in the distal colon of the rat and a model in which Na-hydrogen (H) and Cl-butyrate exchanges are coupled has been proposed as the mechanism of butyrate-dependent electroneutral Na-Cl absorption. These studies were designed to examine butyrate-dependent electroneutral Na-Cl absorption in experimental conditions in which HCO₃-dependent electroneutral Na-Cl absorption is inhibited: in Na-depleted (aldosterone-treated) animals and in the presence of increased mucosal cyclic adenosine monophosphate (AMP). Butyrate-dependent electroneutral Na-Cl absorption was markedly reduced in Na-depleted rats. In contrast, the inhibition of both net Na and net Cl absorption by 5 mM serosal theophylline was significantly less in butyrate-containing, HCO₃-free Ringer solution than in butyrate-free-HCO₃-containing Ringer solution. These studies indicate that cyclic AMP does not inhibit butyrate-dependent electroneutral Na-Cl absorption and we propose that the mechanism of cyclic AMP inhibition of HCO₃-dependent electroneutral Na-Cl absorption may be a result of its inhibition of Cl-HCO₃, not Na-H exchange.     

阿奇霉素-离子交换树脂复合物的制备及其掩味与调控释药作用

为掩盖阿奇霉素(azithromycin,AZI)苦味和个性化调控药物释放速度以减少胃肠道刺激,分别以羟丙基纤维素(hydroxypropyl cellulose,HPC)和尤特奇RS100修饰制备速释型AZI-Amberlite^TM IRP64/HPC和缓释型AZI-Amberlite^TM IRP69/RS100进而组合以实现控制释放。对AZI-离子交换树脂复合物的载药量、药物利用率进行测定,通过差示扫描量热分析和X射线衍射对AZI-离子交换树脂复合物进行结构表征,测定其润湿度、掩味效果、体外溶出和释放行为。结果显示,形成的AZI-离子交换树脂复合物改变了药物原有的结晶状态,2.5%HPC修饰的AZI-Amberlite^TM IRP64/HPC和0.5%RS100修饰的AZI-Amberlite^TM IRP69/RS100掩味效果良好,两者以对应AZI含量为13∶67的比例组合可以实现AZI在前10 min的快速释放和后期的6 h内平稳释药。结果表明,经表面修饰制得的AZI-离子交换树脂复合物及其...     

Solubilization and Stabilization of an Anti-HIV Thiocarbamate,NSC 629243, for Parenteral Delivery,Using Extemporaneous Emulsions

The O-alkyl-N-aryl thiocarbamate, I, (2-chloro-5-[[(l-methyl-ethoxy)thioxomethyl]amino]benzoic acid, 1-methylethylester, NSC 629243, also known as Uniroyal Jr.) is an experimental anti-HIV drug with very low water solubility (1.5 µg/mL). Early clinical studies required an injectable solution at 15 mg/mL, representing a solubility increase of 10⁴-fold. Adequate solubilization of this hydrophobic drug was achieved in 20% lipid emulsions. Extemporaneous emulsions were prepared by adding a concentrated drug solution to a commercially available parenteral emulsion. Various methods of preparation to minimize drug precipitation during its addition and enhance redissolution of precipitated drug were evaluated. The stability and mechanism(s) of decomposition of NSC 629243 in both 20% lipid emulsions and in natural oil vehicles were examined. In lipid emulsions, the shelf life at 25°C varied from 1 to >10 weeks, depending on the extent to which air was excluded from the preparation. The shelf life of 50 mg/mL solutions in natural oils at 25°C varied from <1 to >100 days depending on the oil and its supplier. A qualitative correlation was found between the initial rate of oxidation and the peroxide concentration in the oil. The primary degradation product in both systems was shown to be a disulfide dimer, II, formed via oxidation. Oxidation was inhibited by vacuum-sealing of emulsion formulations or incorporation of an oil-soluble thiol, thioglycolic acid (TGA), into oil formulations. TGA may inhibit oxidation by consuming free radicals or peroxide initiators or by reacting with the disulfide, II, to regenerate the starting drug.